1. Field of the Invention
The present invention relates to a liquid crystal display, and in particular to a liquid crystal display with a supporting base.
2. Description of the Related Art
In FIG. 1, a conventional liquid crystal display on a surface 5 is situated in a stable condition. W is the weight of the display unit 1, and F is external force used for lifting up the display unit 1. The force F is directly on the display unit 1 and rotated the first pivot 22 in a counterclockwise direction.
The liquid crystal display has a display unit 1 and a supporting base 2. The supporting base 2 has a first section 21, a first pivot 22, a second section 23, a second pivot 24, a third section 25 and a plate 26. The first pivot 22 and the second pivot 24 have the same structure, and the first pivot 22 connects the first section 21 and the second section 23, and the second pivot 24 connects the second section 23 and the third section 25. The display unit 1 is connected to the third section 25 by the plate 26. The plate can be integrally formed on the end of third section 25, and the display unit 1 can be directly mounted on the third section 25. Thus, the position of the display unit 1 can be adjusted upwardly or downwardly by rotating the second section 23 around the first pivot 22, and the tilt angle of the display unit 1 can be adjusted by rotating the third section 25 around the second pivot 24.
FIG. 2 is a cross-section of the first pivot 22 of FIG. 1 along its longitudinal direction. The fixed element 211 is a part installed on the first section 21 of the supporting base 2, and the first section is positioned on the surface 5 motionlessly. The movable element 231 is a part installed on the second section 23 of the supporting base 2. A bolt 221 passes through the fixed element 211 and the movable element 231 and is secured by a nut 222. Several washers 224 function as frictional disks between the bolt 221 and the fixed element 211, as well as between the fixed element 211 and the movable element 231. The washers 224 are made of soft material, such as rubber, plastic or the like. A U-shaped washer 223 and another washer 224 are disposed between the movable element 231 and the nut 222. The U-shaped washer 223 is used to keep the washer 224 attaching to the fixed element 211 or the moveable element 231. The U-shaped washer 223 can be made of rigid, flexible material, such as steel, copper or the like.
When the nut 222 rotates toward the head 221 H, the U-shaped washer 223 is pushed and moved toward the washer 224 disposed next to the movable element 231, and the fixed element 211 and the movable element 231 are pressed and pushed to approach each other, bracketed by the deformed washers 224. These deformed washers 224 provide a frictional force to the fixed element 211 and the movable element 231, to balance the weight of the display unit 1.
Referring again to FIG. 1 and also to FIG. 3, as the liquid crystal display is placed on the surface 5, the weight W of the display unit 1 exerts a gravity torque TW by the weight of the display unit 1 on the first pivot 22 in a clockwise direction. In the same time, a static frictional force is generated within the first pivot 22 and exerts a frictional torque TF1 on the first pivot 22 in a counterclockwise direction.
In the first pivot 22, frictional torque TF1 is equal to gravity torque TW (TF1=TW), i.e., the display unit 1 is stable. The static frictional force, however, is variable. The amount of the static frictional force is increased when the external force applied on an object increases. When the static frictional force is increased to a critical value, i.e., maximum static frictional force, the object is moving because of the external force, The frictional force becomes a dynamic friction force, and the value of the frictional force decreases and reaches a constant. In this related art, TF1 is a frictional torque generated by the maximum static frictional force within the first pivot 22.
When the display unit is stable on the surface 5, the direction of the frictional torque TF1 is opposite to that of the gravity torque TW. When an external force is applied to lift the display unit 1, the direction of the frictional torque TF1 is changed. When the display unit 1 is successfully lifted, the torque generated by external force F must overcome the sum of the frictional torque TF1 and gravity torque TW. In FIG. 4, TF2 is a torque generated by the external force F in a counterclockwise direction on the first pivot 22. Thus, torque TF2 must be larger than the sum of frictional torque TF1 and gravity torque TW (TF1+TW). The direction of frictional torque TF1 (clockwise, in FIG. 4) is opposite to the direction of frictional torque TF1 (counterclockwise, in FIG. 3.) because the direction of the maximum static frictional force is changed.
In general, the nut 222 secured on the bolt 221 is tightly driven, such that the washers 224 can be closely attached on the fixed element 211 and the movable element 231, and therefore sufficient frictional force is generated therebetween to balance the weight of the display unit 1. However, the display unit 1 becomes difficult to adjust or position at a predetermined height or angle from the nut 222 on the bolt 221 being over-tightened.
When the nut 222 is tightly connected to the bolt 221, the maximum static frictional force within the first pivot 22 is large and the frictional torque TF1 is also very large. Therefore, the torque TF2, generated by the external force F, used to overcome the frictional torque, is also large.
If the external force F is too big, the first section will also be lifted to leave the surface 5 when adjusting the position of the display unit 1 as shown in FIG. 5. Therefore, another force N is need to apply on the first section 21 of the supporting base 2 to prevent the first section 21 from leaving the surface 5. However, it is inconvenient to manually adjust the position or the angle of the display unit 1.